1. Field of Use
This invention relates generally to large metal structures which serve as component parts of heavy duty mobile machines, such as mining shovels, and to methods for making such structures. In particular it relates to field assembly of such structures from prefabricated subassemblies using electroslag welding techniques.
2. Description of the Prior Art
Certain types of machines, such as mining shovels and the like, are so large physically that it is impossible to construct them in a plant or factory and then ship them in finished form to their final destination, as is the usual practice with smaller machines. Accordingly, it is necessary to prefabricate subassemblies in a factory and ship them, usually by railroad, to some destination such as the final job site, whereat the subassemblies are field assembled into component parts or structures which go to make up the finished machine. This procedure creates several problems which are costly and time-consuming to overcome. For example, the subassemblies being shipped must be limited in size and weight so that they will fit on the railroad cars used for transport. Furthermore, since considerable welding is required to join the subassemblies in the field, it is necessary to provide complete welding facilities in the field which is time-consuming and costly. Factory welding and field welding of large heavy metal components often adapt to the use of electroslag welding techniques and such specialized equipment can be provided for use in the field. It should be noted that, at present, inhouse manufacturing costs are about one-fourth the cost of field assembly, if conventional prior art techniques are followed. Very often, final field assembly of two or more subassemblies require very elaborate jigs to ensure and maintain accurate alignment of the subassemblies as they are being welded together. For example, two adjacent subassemblies may each embody or define accurately machined bearing surfaces, bores, holes or passages which must be accurately positioned relative to each other to ensure proper operation of the finished machine. While such alignment can be expeditiously accomplished in a factory environment where proper facilities, cranes, jigs and tools are readily accessible and permanently installed, it is difficult to meet such requirements in a temporary field installation.
The following patents illustrate some of the problems and practices encountered in the foregoing situation.
U.S. Pat. No. 4,129,773 and 4,104,504 both teach the use of electroslag welding to join together two sections of a large dipper bucket for a mining shovel, Both patents teach a horizontal weld and both appear to employ a conventional mold such as water cooled copper shoes at the sides of the weld. U.S. Pat. No. 4,129,773 is concerned with the materials of which the electroslag welding device is constructed. U.S. Pat. No. 4,104,504 is concerned with a method involving welding base metal of manganese steel by means of a guide and weld wire selected of certain materials. U.S. Pat. No. 4,040,362 is of interest because it teaches a method of constructing a large railway car component from two sub-components and filling a cylindrical metal-receiving void therebetween with weld material. This patent is concerned with electric arc welding as distinguished from electroslag welding. U.S. Pat. No. 4,045,648 is of interest because it shows electroslag welding processes wherein the electrode is withdrawn through passages of various cross-sectional configurations. However, it appears in all cases that at least one side of the passage is defined by some sort of conventional backing material such as copper, aluminium, etc. in the form of a water-cooled shoe.